During various dental and endodontic treatments the pulp within the patient's teeth is exposed or nearly exposed. The tooth pulp is highly sensitive to heat and pressure because it contains the nerve endings of the tooth. Thus, it is desirable to protect this pulp during the filling of cavities, performance of root canals and other dental procedures. Several of the common practices for accomplishing this are described below.
It is known that calcium hydroxide may serve as a protective barrier for pulpal tissue against the attack of acids from certain filling materials used in the teeth by acting as a neutralizing agent. It is also known that calcium hydroxide has a stimulating effect which promotes the healing of dentin by promoting the formation of secondary dentin when the calcium hydroxide is applied near or on the exposed pulp.
For some time, dispersions of calcium hydroxide in aqueous or organic solutions of film-forming materials have been used for the treatment of tooth cavities as the vehicle for contacting the pulp with calcium hydroxide. Typically, however, when calcium hydroxide dispersions in aqueous or organic systems are used, the resultant cavity lining may not have sufficient mechanical strength to protect the tooth from the mechanical impact and stresses which occur during the filling operation.
One means for overcoming the deficiencies of some of the prior aqueous and organic solvent systems containing calcium hydroxide, was the combination of calcium hydroxide within self-hardening pastes. One such self-hardening system is described in U.S. Pat. No. 3,047,408. The '408 patent describes a dental composition that includes excess calcium hydroxide mixed with an ester of a polyhydric alcohol and salicylic acid or its esters. The mixture reacts to form a rigid and permeable mass of calcium phenolate having available calcium hydroxide dispersed therein. Another system of this general type is disclosed in U.S. Pat. No. 4,240,832. The system disclosed in the '832 patent comprises two pastes and is based upon calcium hydroxide and a condensate of an ester of salicylic acid and an aldehyde, such as formaldehyde or its oligomers.
Generally speaking, hardenable systems of the type disclosed in the '408 and '832 patents provide advantages vis-a-vis the earlier calcium hydroxide-containing systems and have found great use as dental cavity liners and pulp capping materials. In these dental cements, the "setting" of the cement is believed to occur through chelation binding of the calcium hydroxide or oxide with the salicylic acid esters to form an ionic lattice structure within the salicylate resin. Because the composition absorbs water, leaching of calcium and hydroxyl ions occurs, which has the beneficial and advantageous properties described hereinabove. However, such hardenable systems have certain disadvantages, including their susceptibility to attack by acids, discoloration, and water sorption.
What is needed are resins and dental compositions which include such resins that can be used to effectively deliver highly alkaline calcium compounds such as calcium hydroxide and/or calcium oxide.